This invention relates in general to firearms and deals more particularly with a handgun having an improved double action firing mechanism which includes a trigger, a movable hammer, and a sear engageable with the trigger. In a handgun of this type, drawing back the trigger causes the hammer to move to a tripping position against the biasing force of a mainspring. At the tripping position the sear disengages from the trigger permitting the hammer to move freely to its striking position in response to the biasing force of the mainspring. In a mechanism of the aforedescribed general type coengageable cam surfaces are usually provided on the trigger and the sear to effect disengagement of the sear from the trigger at the tripping position. However, play between various parts of the mechanism resulting from accumulated manufacturing tolerances and/or wear may cause premature release of the sear from the trigger. This condition results in release of the hammer before the mainspring is fully compressed so that potential energy stored in the mainspring is seriously reduced. This problem is particularly severe in a small handgun, such as a derringer of the so-called "hammerless" type wherein the hammer is concealed within the gun frame and has relatively little room for travel. Premature release of the hammer in a gun of this type is likely to result in misfire. The present invention is concerned with this problem.